1. Field of the Invention
This invention relates to needle assemblies and more specifically to assemblies, such as epidural and anesthesia needle assemblies, that require finger sensitivity and finger control in placement of the cannula in a patient's body.
2. Description of Related Art
Many needle assemblies are known for placing cannulae in the body. In some cases, an incision is cut into the body and a cannula placed therethrough. In others, a cannula is inserted directly into the body. Thereafter, a catheter is placed through the cannula into the body. In many cases it is desirable to use finger control to insert and position the cannula in the body. Often it is desirable to have a great amount of finger sensitivity when placing the cannula in the body to precisely position the cannula. In addition, it is often desirable to have means to readily move the cannula into and out of the body along the elongated axis of the needle assembly.
To satisfy these requirements, needle assemblies having finger manipulation members or "wings" that extend away from the elongated axis of the needle assembly at approximately right angles have been developed. In one method of use, these "wings" allow the physician to grasp the needle assembly with two fingers on the "wing" while placing the thumb on the proximal or non-patient contacting end of the needle assembly. The needle assembly is held by the proximal force put on the wing by the physician's fingers counter balanced by the distal force put on the proximal end of the needle assembly. In this way, distal directed pressure can be applied to the needle assembly by the thumb to push the cannula into the body or the cannula may be moved proximally out of the patient's body by the proximal movement of fingers pulling on the "wings". In addition, the "wings" allow the physician to turn the needle assembly around its elongated axis by rotating his wrist in order to more precisely position the cannula and its typically beveled distal end.
In another method of use, the physician grasps the "wings" with both hands by holding each "wing" between the corresponding thumb and index finger of each hand. In this method, one hand holds the "wing" extending from one side of the needle assembly while the other hand holds the "wing" extending from the other side of the needle assembly. The physician may then either push or pull on the "wings" thereby moving the cannula into or out of the patient's body, respectively. In this method of use, the physician may turn the needle assembly, and consequently the cannula, around its elongated axis by raising or lowering one "wing" relative to the other.
A standard epidural needle assembly is shown in FIG. 1 generally labeled 2. The needle assembly 2 includes a cannula assembly 4 comprising an elongated hollow cannula 6 attached to a needle hub 8. The patient contacting or distal end 10 of cannula 6 typically has a bevel to produce a sharpened end. The needle hub 8, located at proximal end 12 of cannula assembly 4, is finger manipulated by the physician so that cannula 6 may be inserted into the patient's body. A bore 14 extends through needle hub 8 from the proximal end 12 of cannula assembly 4 to the inner bore of cannula 6. A slot 46 extends into needle hub 8 from its proximal end 12. Slot 46 is located along the outer surface of needle hub 8 parallel to bore 14.
Needle assembly 2 also includes a stylet assembly 16. Stylet assembly 16 includes a stylet 18 and a stylet hub 24. Stylet 18 is typically a solid metal rod. The distal end 20 of stylet 18 generally has a bevel corresponding in angle to the angle of the bevel of the distal end 10 of cannula 6.
Stylet hub 24 is located at the proximal end 22 of stylet assembly 16. Stylet hub 24 includes a tang 26 directed toward the distal end 20 of stylet assembly 16. In operation, as will be explained hereafter, when stylet 18 is placed through bore 14 into cannula 6 so that the distal end 20 of stylet 18 is aligned with the distal end 10 of cannula 8, tang 26 will intermesh with slot 46 in needle hub 8 to precisely orient the beveled distal end 20 of stylet 18 with the beveled distal end 10 of cannula 6.
When stylet 18 is fully inserted into cannula 6 and the beveled distal end 20 of stylet 18 and the beveled distal end 10 of cannula 6 are aligned by tang 26 intermeshing with slot 46, a flat surface is presented across the beveled distal ends 10,20 of cannula 6 and stylet 18, respectively. This provides a substantially closed surface at the distal end 10 of cannula 6 to prevent coring of the patient while inserting the cannula 6 into the patient.
Stylet hub 24 also includes a thumb piece 28 located on the proximal end 22 of stylet assembly 16. Thumb piece 28 allows the physician to move stylet assembly 16 distally by pushing on thumb piece 28 with the physician's thumb.
A protective sheath 30, typically comprising a rigid cylindrical plastic tube, is provided to encase cannula 6 when not in use and prevent inadvertent contact with the sharp beveled distal end 10. Protective sheath 30 has a proximal end 32 that contacts a protective sheath mount 36 located at the distal end of needle hub 8. When protective sheath 30 is in position over cannula 6 so that the proximal end 32 is in contact with protective sheath mount 36, protective sheath 30 is sufficiently long so that the distal end 34 of protective sheath 30 extends beyond the distal end 10 of cannula 6. In this way, persons and objects are protected from unwanted contact with the sharp distal end 10 of cannula 6 by the covering of the rigid protective sheath 30. Protective sheath 30 is removed prior to the physician inserting cannula 6 into the patient's body.
Many epidural or anesthesia needle systems 2 have a wing 38 mounted on needle hub 8. Typically, wing 38 is a thin, substantially planar device that extends away from the main axis of needle hub 8 at substantially a right angle near the distal end of needle hub 8.
Many epidural or anesthesia needle assemblies 2 attach wings 38 to needle hub 8 permanently; in the case of metal needle assemblies 2, the wings 38 are soldered to the needle assembly 2. However, it is often desirable to be able to selectively remove wing 38. Therefore, wings 38 that may be removed from needle hub 8 are known.
One typical way to attach wing 38 to needle hub 8 is to form a slot in needle hub 8, substantially aligned with the plane of wing 38. A corresponding tab is formed on wing 38 to slide into and be constrained by the slot. However, a problem with this system for attaching wing 38 to needle hub 8 is that either proximal or distal pressure on wing 38 by the physician causes wing 38 to deform. As a result of wing 38 deforming, the tabs on wing 38 move out of constraining contact with the slot in needle hub 8, thereby detaching wing 38 from needle hub 8. Besides creating an annoying condition for the doctor, the condition is also potentially unsafe because the physician has temporarily lost control of the cannula 6 in the patient's body. Therefore it is highly desirable to provide an epidural or anesthesia needle assembly 2 with detachable wings 38 where the wings 38 may be securely fastened to the needle hub 8, yet easily removed if desired.
As stated, a problem with some prior art epidural needle assemblies 2 having wings 38 is that the wings 38 are integrally connected to the cannula. Consequently, in applications where it is desired that the epidural needle assemblies 2 be used without wings 38, a separate version of the epidural needle assembly 2 must be produced; one having and one not having wings 38. This leads to production duplication and inventory and storage problems. As a result, it is desirable to make an epidural needle assembly that may or may not be used with "wings" as desired.